Typically, sleeping bags are used when conventional bed and bedding are unavailable. For example, sleeping bags are used by backpackers, hikers, campers, mountaineers, and other users as portable beds or coverings. Sleeping bags are often durable sleeping coverings that provide a soft surface, insulation, and weather resistance.
Consumers face a difficult task in finding a sleeping bag that is thermally efficient, comfortable, and lightweight. One type of sleeping bag is referred to as a “mummy bag”, which tends to be shaped with a lateral taper to approximate the contour of the body of a user and thereby minimize the internal volume of the bag. Mummy bags attempt to conserve heat by minimizing air movement within and from the bag. As a result, mummy bags are often suited for use in outdoor, colder ambient temperatures. One drawback to the mummy bag is that some users may feel discomfort due to the tight fit of the bag. Some users may become too warm or the air within the bag may become stagnant. Such feeling of discomfort may be increased in the foot portion of the bag due to its distance from the opening of the bag. Thus, some users are unable to sleep comfortably in mummy bags.
Other sleeping bags, such as rectangular-type sleeping bags, are shaped with a generally constant lateral dimension and provide a greater range of motion for the user. Such bags also typically have a zippered portion to allow the user to more easily enter the bag. However, although rectangular bags are often more spacious than mummy bags, one drawback is that the larger internal volume reduces the thermal efficiency of the bag. Moreover, rectangular bags often do no insulate the head, and are typically too large to be thermally efficient. As a result, rectangular bags tend to be better suited for use indoors or in milder outdoor temperatures. When used in outdoor, colder ambient temperatures, air within the bag can more easily become chilled, especially in the foot portion of the bag.
Accordingly, a need exists for a sleeping bag that is both comfortable, thermally efficient, and allows the warm, stagnant air within the bag to escape and be replaced with fresh, ambient air.